1. Field of the Invention
The present invention relates to an optical switch, and in particular to an optical switch which outputs an optical signal of a plurality of wavelengths, which is multiplexed.
2. Description of the Related Art
In an optical fiber communication, a wavelength division multiplexing (WDM) communication has been hitherto performed widely. In the wavelength division multiplexing (WDM) communication, by using a plurality of lights of different wavelengths, an independent signal is subjected to a multiplex transmission, and a transmission capacity per optical fiber is increased. In the wavelength division multiplexing communication, in each node for each signal, in other words for each wavelength, a switch for selecting a subsequent transmission-destination node is necessary.
For example, in U.S. Pat. No. 6,625,346, an optical switch used with such an object is disclosed. Wavelength-multiplexed light incident from an input fiber is subjected to spectral separation at a grating. The light subjected to the spectral separation forms an image on an MEMS (Micro Electro Mechanical System) mirror according to each of the wavelengths. Moreover, an angle of inclination of the MEMS mirror is changed. Accordingly, an output fiber can be switched (selected) according to the wavelength. By such optical switch, for each optical signal, in other words, for each wavelength, an optical fiber of an output destination can be selected without performing an optical-to-electrical conversion.
A control of an angle of the mirror in the optical switch described in U.S. Pat. No. 6,625,346, first of all, extracts a partial quantity of light at a tap. Further, the light extracted is monitored at a spectral monitor. Accordingly, the control of the angle is performed according to the wavelength, in other words, according to the mirror.
In such an optical switch of a conventional technology, for controlling an angle of inclination of the mirror, a tap and a spectral monitor are required to be provided outside. Therefore, such optical switch causes an increase in an optical loss. Furthermore, due to installation of the spectral monitor, there is an increase in a size and a cost of the apparatus.